The present invention relates to a scaffolding system for volumes of various shapes, and particularly but not exclusively for use in lagging the tanks of liquefied gas tanker ships.
More generally, the invention relates to scaffolding systems that can be put in place inside enclosures whose walls can present a wide variety of shapes, and in particular can be spherical, cylindrical, of polygonal vertical section, or indeed a combination of such shapes.
This problem is to be found in particular when applying the thermal insulation or xe2x80x9claggingxe2x80x9d to tanks in ships used for transporting liquefied gas.
Accompanying FIGS. 1A and 1B are a longitudinal section and a cross-section through a ship for transporting liquefied gas. The ship 10 has a plurality of tanks 12, 14, 16, and 18 disposed along the length of its hull. When the ship is being built and after the tanks have been made, at least once the main walls 20 thereof have been made, it is necessary to lag these walls 20 with an insulating structure, possibly constituted by a plurality of layers of material. FIG. 1B is a cross-section through a typical shape for such a tank 14. It comprises a floor or bottom 20, a ceiling 26 having an access opening 30, and vertical side walls 22 and 24. The floor 20 is connected to the side walls via bottom sloping walls 32 and 34, while the ceiling 26 is connected to the side walls via top sloping walls 36 and 38. The tank also has a vertical front wall 35 and a vertical rear wall 37.
It will be understood that with such tanks, or more generally with similar enclosures, the problem when making scaffolding consists firstly in the difficulty of gaining access to the enclosure and secondly in the unusual and irregular shape of the walls which the scaffolding is to face once it has been erected.
It will also be understood that when building a ship for transporting liquefied gas, the time required for building is a parameter that is economically decisive. It is therefore very desirable for shipyards to have scaffolding systems for putting into place, in particular inside tanks, which systems should be suitable for being put into place and then dismantled relatively quickly and should be suitable for use with the particular shape of the walls to which the scaffolding system is intended to give access.
Furthermore, in order to obtain a better understanding of the problem posed, it needs to be recalled that the width of the tank can be about 30 meters (m), that the length of the tank can be about 40 m and that the height of the tank is likewise about 30 m. It can thus be seen that the area of the walls to which the scaffolding system is to give access is very large.
Accompanying FIG. 1C is a cross-section through another volume shape which also requires scaffolding to be put into place for lagging its walls. This tank comprises a wall 11 and a coffer 13. In right section, the wall comprises a bottom 21, side walls 23 and 25, and a ceiling 27 pierced by an access opening 28. Top sloping walls 29 and 31 and bottom sloping walls 33 and 39 interconnect the side walls with the ceiling and the bottom.
It will be understood that installing scaffolding inside such a tank raises special problems.
In patent application WO 93/20307, scaffolding is described for working inside the tank of a methane tanker, which scaffolding comprises a carrier structure made up of two legs interconnected by cross-members forming a gantry, and by a large number of modular platforms mounted at various heights and cantilevered out from the outside face of said legs.
Such a structure requires erection time that is lengthy insofar as it must be made along the entire length of the tank and insofar as it requires a very large amount of scaffolding material, in particular for making the modular platforms.
Document U.S. Pat. No. 4,057,943 also describes a scaffolding structure, in particular for the tanks of a methane tanker, in which a carrier structure is assembled inside the tank, the structure standing on the bottom of the tank and carrying a set of platforms including adjustable ends for giving access to the different portions of the inside wall of the tank.
An object of the present invention is to form a scaffolding system for volumes of various shapes and in particular for tanks for storing or transporting liquefied gas, enabling the scaffolding to be put into place quickly inside the volume and making the scaffolding easy to use without requiring a large quantity of scaffolding elements to be involved.
The invention achieves this object by means of a scaffolding system for volumes of various shapes presenting a bottom and end walls, the system being characterized in that it comprises at least a first scaffolding structure comprising:
a gantry-forming structure comprising at least two vertical poles interconnected to form a gantry, each of said poles having a bottom end;
means secured to said bottom of the volume to guide said bottom ends of the poles in rectilinear displacement in a longitudinal direction on said bottom;
means forming a horizontal main platform and means for guiding said main platform-forming means in vertical translation along said poles, said platform-forming means having two end edges in a direction orthogonal to the displacement direction of said gantry;
at least two horizontal auxiliary platforms mounted to move in horizontal translation relative to said main platform, each platform having an outer edge; and
means for displacing each auxiliary platform separately relative to the main platform between a retracted position in which the outer edge of the auxiliary platform is retracted relative to the outer edge of the main platform, and an extended position in which the outer edge of the auxiliary platform is substantially vertically in register with the outer edge of the main platform.
It will be understood that this scaffolding system has three degrees of freedom to give access to all of the portions of the wall of the volume in which the scaffolding is erected. Longitudinal displacement of the gantry-forming structure constitutes one degree of freedom in the length direction of the volume, vertical displacement of the main platform relative to the gantry constitutes a second degree of freedom in the height direction of the volume, and the ability of the two auxiliary platforms to be displaced relative to the main platform enable the outline of the scaffolding to be matched to the different portions of the wall of the volume at different levels.
In a preferred embodiment, the scaffolding system further comprises at least second and third scaffolding structures very similar to said first scaffolding structure. These two scaffolding structures make it possible to work on the extreme front and rear walls of the tank, the moving first scaffolding structure making it possible to work on the side walls between the two end structures.
Preferably, the edges of the end scaffolding structures facing the end wall have respective telescopic extensions.